The quantum mechanical fluctuations in the inflaton field
produce adiabatic fluctuations. Provided anistropic stresses
in the primordial plasma are small, as is normally the case,
\(\Psi (\vec{k},t) = - \Phi (\vec{k},t)\)  [1]}. We
will assume this to be true henceforth. The power spectrum
of \(\Phi \)  fluctuations when they reenter the horizon
(k = a(t) H(t)) is
\(<\Phi (\vec{k},t) \Phi ^*(\vec{k}^\prime ,t)>|_{k = a H}\equiv <\Phi _p(\vec{k}) \Phi _p^*(\vec{k}^\prime )> =(2 \pi )^3 \delta (\vec{k} - \vec{k}^\prime ){8 \pi G \over 9 k^3} {H_I^2 \over \epsilon }\) 
